Last breeding season (April-June), the WFVZ teamed up with Cooper Ecological Monitoring, Inc. (CEM) and the California Department of Fish and Game (CDFG) to collect distribution, occupancy, and nesting data on Ventura County’s resident Cactus Wrens (Campylorhynchus brunneicapillus), which represent the western-most extension of the species’ range (see our previous newsletter for further details). Surveys of this sort have never been conducted for the local Wrens, even though Ventura County contains some of southern California’s largest remaining coastal cactus scrub. The survey relied on the participation of nearly 30 volunteers who were essential in bringing this “citizen science” project to fruition. Results have been summarized in a report sent to the CDFG (summary below), and a paper detailing the species’ status in Ventura County is being prepared for publication in the Western Field Ornithologist’s journal, Western Birds.
By the survey’s end, participants detected 117 active or probable Cactus Wren territories; California Gnatcatchers also were detected at 14 Cactus Wren sites. The current core range of Cactus Wrens within Ventura County appears to be restricted to soils derived from the Conejo Volcanics where they experience strong coastal influence. Within this relatively narrow band, south facing slopes bear the largest concentrations of suitable prickly pear habitat and, consequently, the most active territories. This approximate range extends from the western edges of Simi Valley southwest along the western edge of Thousand Oaks, then south along the Santa Monica Mountain’s southern edge to the vicinity of Point Mugu. The species formerly occupied habitat in the Santa Clara River Valley, but appears to have been extirpated. Curiously, the range of the California Gnatcatcher, including historical records from the Santa Clara River, follows a very similar pattern within the County.
Similar studies were previously conducted in Los Angeles, Orange, and San Diego counties; in the latter two, the Cactus Wren is listed as a California Species of Special concern (C. brunneicapillus sandiegense). Ventura County Cactus Wrens (and those on the coastal slope of Los Angeles County) have long been considered an isolated pocket of the widespread desert subspecies, anthonyi, which perhaps travelled southwest through the Santa Clara River drainage from the high deserts of Los Angeles county. The taxonomy and population status of coastal Cactus Wrens in Ventura County have implications for future conservation work and land management decisions. We look forward to future collaborations with CEM, CDFG, and other interested agencies on Cactus Wrens and other projects within Ventura County, and we would like to extend special thanks to all of the volunteers and employees who assisted with this project.